Sepsis is a systemic inflammatory response syndrome (SIRS) induced by infection. Specifically, sepsis is defined as a pathological condition that meets, in addition to the presence of infection, two or more of the SIRS items ((1) body temperature >38° C. or <36° C., (2) heart rate >90/minute, (3) respiration rate >20/minute, or PaCO2 <32 torr, and (4) leucocyte count >12,000/μL or <4000/μL, or immature leucocytes >10%). Although presence of bacteria in blood (bacteremia) has been significantly focused so far, bacteria-positive result of blood culture is not necessarily required according to the above definition. Among sepsis, a condition presenting organ dysfunction, organ hypoperfusion, or hypotension is called severe sepsis. The organ hypoperfusion or abnormal perfusion includes lactic acidosis, oliguria, mental clouding, and the like. Among the severe sepsis, a condition continuously presenting hypotension despite of sufficient load of fluid therapy is called septic shock (Non-patent document 1). It is considered that the circulatory failure observed in these pathological conditions is caused by malfunction of the sympathetic nervous system or a mediator released from neutrophiles and the like, and the organ dysfunction is caused by tissue hypoxia (dysoxia).
Thrombomodulin has been known as a substance that acts to specifically bind to thrombin so as to inhibit the blood coagulation activity of thrombin, and at the same time, exerts anticoagulant activity so as to significantly promote the ability of thrombin to activate Protein C. It has also been known that thrombomodulin exerts to prolong the clotting time by thrombin, or suppresses platelet aggregation by thrombin. Protein C is a vitamin K-dependent protein that plays an important role in a blood coagulation and fibrinolysis, and activated by the action of thrombin to be converted as activated Protein C. It has been known that the activated Protein C inactivates activated blood coagulation factor V and activated blood coagulation factor VIII in vivo, and is involved in generation of a plasminogen activator having thrombolytic action (Non-patent document 2). Accordingly, it has been considered that thrombomodulin promotes the activation of Protein C by thrombin, and therefore is useful as an anticoagulant or a thrombolytic agent. It has also been reported that, in an animal experiment, thrombomodulin is effective for therapy or prophylaxis of diseases associated with hypercoagulable state (Non-patent document 3).
Thrombomodulin was first discovered and obtained as a glycoprotein expressed on the vascular endothelial cells of various animal species including humans, and then successfully cloned. Specifically, a gene of a human thrombomodulin precursor including a signal peptide was cloned from a human lung cDNA library by genetic engineering techniques and the entire gene sequence of thrombomodulin was analyzed, and as a result, an amino acid sequence consisting of 575 residues containing a signal peptide (in general, 18 amino acid residues are exemplified) was revealed (Patent document 1). It is known that a mature thrombomodulin, from which the signal peptide is cleaved, is composed of 5 regions, namely, an N-terminal region (amino acid residues 1 to 226, these positions are defined under an assumption that the signal peptide consists of 18 amino acid residues, and the same shall apply to the following descriptions), a region having six EGF-like structures (amino acid residues 227 to 462), an O-linked glycosylation region (amino acid residues 463 to 498), a transmembrane region (amino acid residues 499 to 521), and an cytoplasmic region (amino acid residues 522 to 557), from the N-terminal side of the mature peptide. It is also known that a partial protein having the same activity as that of the entire length thrombomodulin (i.e., a minimal active unit) is mainly consisting of the 4th, 5th, and 6th EGF-like structures from the N-terminal side in the region having six EGF-like structures (Non-patent document 4).
The entire length thrombomodulin is hardly dissolved in the absence of a surfactant, and addition of a surfactant is essential for manufacturing an entire thrombomodulin preparation. A soluble thrombomodulin is also available that can be fully dissolved even in the absence of a surfactant. The soluble thrombomodulin may be prepared by removing at least a part of the transmembrane region or the entire transmembrane region. For example, it has been confirmed that a soluble thrombomodulin consisting of only 3 regions, namely, the N-terminal region, the region having six EGF-like structures, and the O-linked glycosylation region (i.e., a soluble thrombomodulin having an amino acid sequence consisting of amino acid residues 19 to 516 of SEQ ID NO: 9) can be obtained by applying recombination techniques, and that the resulting recombinant soluble thrombomodulin has the same activity as that of an entire thrombomodulin (Patent document 1). Some other reports are also available regarding soluble thrombomodulins (Patent documents 2 to 9). A human urine-derived soluble thrombomodulin and the like are also exemplified as native thrombomodulins (Patent documents 10 and 11).
As recognized in many cases, as a result of spontaneous mutations or mutations occurring at the time of obtainment, polymorphic mutations have been found in the human genes. At present, thrombomodulin proteins in which the amino acid at the position 473 of human thrombomodulin precursor having the amino acid sequence consisting of 575 amino acid residues is converted to Val or Ala have been identified. In the nucleotide sequence encoding the amino acid sequence, this variation of amino acid residue corresponds to mutation to T or C at the position 1418 (Non-patent document 5). However, the two types of thrombomodulins are completely identical in terms of their activity and physicochemical properties, and it can be considered that they are substantially identical.
It has been reported that thrombomodulin is effective for a therapeutic treatment of disseminated intravascular coagulation (henceforth also referred to as DIC) (Non-patent document 6). As for use of thrombomodulin, in addition to the aforementioned use, thrombomodulin is expected to be used in therapeutic and prophylactic treatments of various diseases such as acute coronary syndrome (ACS), thrombosis, peripheral vessel obstruction, obstructive arteriosclerosis, vasculitis, functional disorder occurring after heart surgery, complication caused by organ transplantation, angina pectoris, transient ischemic attack, toxemia of pregnancy, diabetes, liver VOD (liver veno-occlusive disease, e.g., fulminant hepatitis, veno occlusive disease of liver occurring after bone marrow transplantation), and deep venous thrombosis (DVT), and further, sepsis and adult respiratory distress syndrome (ARDS) (Patent document 12).